Cobaltosic oxide and cobalt carbonate and preparation methods therefor, positive electrode material and lithium-ion battery

Abstract

The present disclosure relates to the technical field of new energy. Provided are cobaltosic oxide and cobalt carbonate and preparation methods therefor, a positive electrode material and a lithium-ion battery. Cobalt carbonate and corresponding cobaltosic oxide secondary particles are integrally subjected to gradient doping with Al, and the Al doping amount of a core layer thereof is higher than that of a coating layer, such that the crystal structure stability of an LCO material is improved, and the cycle performance of a lithium cobaltate battery prepared from a sintered positive electrode material is improved. The cobaltosic oxide comprises a core layer and a coating layer that coats the core layer, wherein the content of cobalt is reduced layer by layer from inside to outside, such that the surface Co4+ content is reduced, the Co dissolution amount is decreased, and the safety performance can be improved. The core layer is a functional layer, takes up a large proportion by volume, has a high cobalt content, and can improve the capacity and the cycle performance; and the coating layer is a modified layer, coats the core layer and is very thin, and the total content of doping elements is increased in a gradient manner, such that the specific performance of the material can be improved, and the comprehensive performance of LCO can be improved.

Description

Cobaltous oxide, cobalt carbonate and preparation method, positive electrode material and lithium ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to Chinese patent application number 202310622177.4 filed with the Patent Office of China on May 30, 2023, entitled “A cobalt trioxide, cobalt carbonate and preparation method, positive electrode material, and lithium-ion battery,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to the field of new energy technology, and in particular to cobalt tetroxide, cobalt carbonate and preparation methods, positive electrode materials, and lithium-ion batteries. Background Art

[0004] With the rapid development of technology, portable mobile devices have become ubiquitous in our daily lives, and people's requirements for mobile devices' battery life, size, and fast charging capabilities have also increased. Lithium cobalt oxide batteries, with their high volumetric energy density and other advantages, are widely used in the field of 3C digital products.

[0005] The battery life and cycle life of lithium cobalt oxide (LCO) batteries in lithium-ion secondary batteries are of widespread concern within the industry. Currently, the theoretical specific capacity of LCO at 4.2V is 274mA / g. While current voltages can reach above 4.4V, the actual capacity is only 180mA / g, and this capacity significantly decreases with increasing cycles. To achieve higher capacity, LCO is being developed towards higher voltages above 4.5V. This is because at higher voltages, more lithium ions are released from the crystal structure, thereby increasing LCO capacity.

[0006] At present, the industry generally adopts the doping method to improve the structural stability of the material under high voltage by changing the crystal structure of LCO (lithium cobalt oxide) material. However, as the types and amounts of doping elements increase, the uniformity of doping elements in LCO becomes very important. Otherwise, the capacity and cycle performance of battery materials will decrease due to uneven doping.

[0007] In addition, due to the diversity of application scenarios of lithium-ion secondary batteries, in addition to the requirements for high capacity and long cycle core functions, differentiated demands will also arise. Among lithium cobalt oxide positive electrode materials, cobalt tetroxide is its most important raw material. The performance of cobalt tetroxide determines the performance of lithium cobalt oxide to a certain extent, which also puts forward different requirements for the positive electrode material precursor, such as improving rate performance and more outstanding cycle performance.

[0008] How to ensure the uniformity of doping elements in LCO for different application scenarios of lithium-ion secondary batteries while taking into account battery capacity and core cycle functions, while meeting the differentiated needs of different customers through a set of adjustable technical solutions, has become a technical problem that urgently needs to be solved in this field.

[0009] Summary of the Invention

[0010] The purpose of the present disclosure is to solve the above-mentioned technical problems and provide a cobalt oxide, cobalt carbonate and preparation method, positive electrode material, and lithium-ion battery. While ensuring that the core layer meets the high capacity and long cycle functions, the number of layers of the coating layer and the type and content of doping elements can be adjusted according to the differentiated needs of different customers through a set of adjustable technical solutions to prepare products that meet the needs of different customers.

[0011] To achieve the above objectives, the first aspect of the present disclosure provides a cobalt oxide, comprising a core layer and a coating layer coated outside the core layer, as shown in Figure 40; the core layer and the coating layer are both doped with Al, and the Al doping content of the core layer is higher than the Al doping content of the coating layer; that is, the total Al doping content of the core layer is higher than the total Al doping content of the coating layer; schematically, when the coating layer is multi-layered, the total Al doping content of the coating layer is the total Al doping content of multiple coating layers, and the total content can be the total mass or the total molar amount, the same below.

[0012] The stratification standard of the cobalt carbonate core layer and the coating layer involved in the present application is: stratification is carried out according to the different types and / or contents of the doping elements in different areas of the cobalt carbonate, the innermost layer is divided into the core layer, and the layer coated outside the core layer is divided into the coating layer; for example, it can be divided into a core layer with a large proportion and a coating layer with a small proportion according to different doping aluminum contents; it can also be divided into a core layer and a single-layer coating layer, or a core layer and a multi-layer coating layer according to the different types and contents of the doping elements; wherein, the types and contents of the doping elements can first be analyzed by an electron probe instrument for the types of elements and the corresponding content distribution in the cross-section micro-area, and then the specific doping element content can be determined by an ICP (inductively coupled plasma spectrometer); more specifically, as shown in FIG. As shown, the core layer is doped with Al and may also be doped with Ni and Mn; the cladding layer may be 1-5 layers, the cladding layer is doped with Al, and may also be doped with Zr, La, Y, Ti, and Mg; the contents of the above-mentioned doping elements in different layers may also be different; or as shown in FIG41 , it is divided into 6 layers: a core layer and 5 cladding layers; wherein, the core layer is doped with Al and Ni; the cladding layer n1 coated outside the core layer is doped with Al and Zr, the cladding layer n2 coated outside the cladding layer n1 is doped with Al and La, the cladding layer n3 coated outside the cladding layer n2 is doped with Al and Y, the cladding layer n4 coated outside the cladding layer n3 is doped with Al and Ti, and the cladding layer n5 coated outside the cladding layer n4 is doped with Al and Mg.

[0013] The layering standards of the cobalt oxide core layer and the coating layer involved in this application are divided according to the corresponding cobalt carbonate layering.

[0014] The cobalt oxide provided by the present disclosure includes a core layer and a coating layer coated outside the core layer. By Al doping the entire cobalt oxide particle, and the Al doping amount of the core layer is higher than that of the coating layer, the crystal structure stability of the LCO material can be improved and the cycle performance can be improved.

[0015] Preferably, the cobalt content of the cobalt trioxide decreases layer by layer from the core layer to the coating layer.

[0016] The coating layer of cobalt tetroxide is a functional layer. By increasing the total doping element content in each layer, the specific performance of the cathode material after sintering is improved, and the comprehensive performance of LCO after sintering is improved. The cobalt content in the product decreases layer by layer from the inside to the outside, which can reduce the surface Co 4+ content, reduce Co dissolution and improve safety performance.

[0017] Preferably, the cobalt trioxide satisfies at least one of the following conditions A to H:

[0018] A. The coating layer of cobalt trioxide is 1 to 5 layers, for example, 1 layer, 2 layers, 3 layers, 4 layers or 5 layers or 2-4 layers, or 3-5 layers;

[0019] B. The ratio of the mass of doped Al in the core layer of the cobalt oxide to the total mass of the metal in the core layer of the cobalt oxide is: 0.40-1.20wt%, for example, 0.40-0.80wt%, or 0.80-1.00wt%, or 1.00-1.20wt%, or 0.70-1.10wt%, more specifically, for example, 0.40wt%, 0.50wt%, 0.60wt%, 0.70wt%, 0.80wt%, 0.85wt%, 0.90wt%, 0.95wt%, 1.00wt%, 1.05wt%, 1.10wt% or 1.20wt%;

[0020] C. The ratio of the mass of doped Al in the coating layer of cobalt oxide to the total mass of metal in cobalt oxide is: 0.02-0.40wt%, for example, 0.02-0.1wt%, or 0.05-0.15wt%, or 0.1-0.4wt%, or 0.03-0.07wt%, more specifically, for example, 0.02wt%, 0.05wt%, 0.08wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt% or 0.4wt%;

[0021] The method for determining the ratio of the mass of doped Al in the cobalt tetroxide coating layer to the total metal mass in the cobalt tetroxide involved in the present application is: sintering a cobalt carbonate core layer and a cobalt carbonate into a cobalt tetroxide core layer and cobalt tetroxide, respectively; then determining the mass fraction of the mass of Al in the cobalt tetroxide core layer and the cobalt tetroxide to the total metal mass, respectively; and then subtracting the mass fraction of the mass of Al in the cobalt tetroxide core layer to the total metal mass from the mass fraction of Al in the cobalt tetroxide core layer to the total metal mass to obtain the difference, which is the metal mass ratio of the doped element Al in the cobalt tetroxide coating layer to the cobalt tetroxide.

[0022] D. When the cobalt oxide coating layer is one layer, the ratio of the molar amount of cobalt in the coating layer to the total molar amount of metal in the cobalt oxide coating layer is ≤70 mol%, for example, 50 mol%, 55 mol%, 60 mol%, 65 mol%, 67 mol%, 69 mol% or 70 mol%;

[0023] E. When the number of cobalt oxide coating layers is 2 to 5, the ratio of the molar amount of cobalt in the outermost layer of the coating layer to the molar amount of the total metal in the outermost layer of the cobalt oxide coating layer is ≤ 70 mol%, for example, 50 mol%, 55 mol%, 60 mol%, 65 mol%, 67 mol%, 69 mol% or 70 mol%;

[0024] F. The diameter of the core layer of cobalt trioxide is 5.0 to 18.0 μm, for example, 5.0 to 8.0 μm, or 8.0 to 10.0 μm, or 10.0 to 13.0 μm, or 13.0 to 18.0 μm, or 15.0 to 17.0 μm, and more specifically, for example, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, or 18.0 μm;

[0025] G. When the coating layer of cobalt trioxide is one layer, the thickness of the coating layer is 0.10 to 1.0 μm, for example, 5.0 to 8.0 μm, or 8.0 to 10.0 μm, or 10.0 to 13.0 μm, or 13.0 to 18.0 μm, or 15.0 to 17.0 μm, and more specifically, for example, 0.10 μm, 0.15 μm, 0.20 μm, 0. 25μm, 0.30μm, 0.35μm, 0.40μm, 0.45μm, 0.50μm, 0.55μm, 0.60μm, 0.65μm, 0.70μm, 0.75μm, 0.80μm, 0.85μm, 0.90μm, 0.95μm or 1.0μm; wherein the thickness of the coating layer is the difference in particle size D50 before and after each coating;

[0026] H. When the coating layer of cobalt trioxide is 2 to 5 layers, the thickness of a single layer in the coating layer is 0.10 to 1.0 μm, for example, 0.10 to 0.30 μm, or 0.30 to 0.40 μm, or 0.40 to 0.50 μm, or 0.50 to 0.70 μm, or 0.70 to 1.0 μm, or 0.2 to 0.5 μm, or 0.1 to 0.4 μm. More specifically, For example, it may be 0.10 μm, 0.15 μm, 0.20 μm, 0.25 μm, 0.30 μm, 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, 0.55 μm, 0.60 μm, 0.65 μm, 0.70 μm, 0.75 μm, 0.80 μm, 0.85 μm, 0.90 μm, 0.95 μm or 1.0 μm.

[0027] Preferably, the cobalt trioxide satisfies at least one of the following conditions I to L:

[0028] I. The core layer of cobalt trioxide also includes Ni and / or Mn;

[0029] J. When condition I is met, the ratio of the mass of Ni and Mn doped in the core layer of the cobalt oxide to the total metal mass in the core layer of the cobalt oxide is independently 0.10-3.00 wt%, for example, 0.10-0.80 wt%, or 0.80-1.50 wt%, or 1.50-3.00 wt%, or 0.10-0.30 wt%, more specifically 0.10 wt%, 0.50 wt%, 0.8 wt%, 1.00 wt%, 1.20 wt%, 1.30 wt%, 1.40 wt%, 1.50 wt%, 1.60 wt%, 1.70 wt%, 1.80 wt%, 1.90 wt%, 2.00 wt%, 2.10 wt%, 2.20 wt%, 2.30 wt%, 2.40 wt%, 2.60 wt%, 2.80 wt% or 3.00 wt%;

[0030] K. The cobalt oxide coating layer further includes one or more doping elements selected from the group consisting of Mg, Ti, La, Zr, Y, Ca, Sr, and Ba;

[0031] That is, in addition to being doped with Al, the coating layer of cobalt trioxide may be a layer doped with one of the above elements, or a layer doped with multiple elements. More specifically, when the coating layer is a single layer, in addition to being doped with Al, it may be doped with one of the above elements other than Al, or may be doped with multiple elements other than Al. When the coating layer is a multilayer layer, in addition to being doped with Al, it may be doped with only one of the above elements other than Al in each coating layer, or may be doped with multiple elements other than Al in each coating layer.

[0032] Preferably, when the coating layer is two layers, the coating layer is divided into an inner layer and an outer layer, the inner layer of the coating layer further includes one or more of Zr, La, Ca, Ba, Y, Ti, and Sr; the outer layer of the coating layer further includes one or more of Mg, Zr, Ti, and Sr;

[0033] When the coating layer has 3-5 layers, the coating layer is divided into an inner layer, an intermediate layer and an outer layer, the inner layer and the outer layer are respectively 1 layer, and all layers other than the inner layer and the outer layer are intermediate layers, the inner layer of the coating layer further includes one or more of Zr, La, Ca, and Ba; the intermediate layer of the coating layer further includes one or more of La, Zr, Y, Ti, and Sr; and the outer layer of the coating layer further includes one or more of Mg, Zr, Ti, and Sr;

[0034] Among them, La and Zr form a stable solid phase layer, Ca and Ba doping replace part of Co, play a role in stabilizing the skeleton structure, and are more suitable for being placed in the inner layer or middle layer; La and Zr have large ion radius, which can increase the C axis distance of the unit cell and facilitate ion migration; Y, Ti, and Sr can all improve electrical conductivity, facilitate ion migration, and improve rate performance, and are more suitable for being placed in the inner layer or middle layer; Mg and Sr doping can effectively improve electrical conductivity, and the Mg / Ti mixed structure can inhibit material phase change and improve surface structure stability;

[0035] L. When condition K is met, the ratio of the mass of other doping elements except Al in the coating layer of cobalt oxide to the total metal mass in cobalt oxide is independently: 0.01-0.40wt%, for example, it can be 0.01-0.15wt%, or 0.15-0.30wt%, or 0.30-0.40wt%, or 0.04-0.12wt%, or 0.02-0.14wt%, more specifically, for example, it can be 0.01wt%, 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.10wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.15wt%, 0.12wt%, 0.13 ... .06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.10wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt%, 0.20wt%, 0.22wt%, 0.24wt%, 0.28wt%, 0.30wt%, 0.32wt%, 0.34wt%, 0.36wt%, 0.38wt% or 0.40wt%.

[0036] The test method for the ratio of the mass of other doping elements other than Al in the coating layer of cobalt tetroxide involved in this application is: cobalt carbonate is sintered into cobalt tetroxide, and then the measured mass fraction of other doping elements other than Al in the cobalt tetroxide is divided by the total metal mass fraction in the cobalt tetroxide, which is the ratio of the mass of other doping elements other than Al in the coating layer of cobalt tetroxide to the total metal mass in the cobalt tetroxide.

[0037] Preferably, cobalt trioxide satisfies at least one of the following conditions M to Q:

[0038] M. The porosity of the core layer of cobalt oxide is 5.5-9.5%, for example, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0% or 9.5%; or 5.5-6.5%, 6.5-7.5%, or 7.5%-8.5%, or 8.5-9.5%. The overall porosity of cobalt oxide is 4.5-7.5%, for example, 4.5%-5.0%, or 5.0%-5.5%, or 5.5%-6.0%, or 6.0%-7.5%, or 4.5-6.0%. , more specifically, for example, 4.5%, 4.8%, 4.9%, 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.2%, 7.4%, 7.6%, 7.8%, 8.0%, 8.2%, 8.4%, 8.6%, 8.8%, 9.0%, 9.2%, 9.4% or 9.5%;

[0039] N. The pore volume of the core layer of cobalt tetroxide is 0.004~0.015cm 3 / g, for example, 0.004 to 0.008 cm 3 / g, or 0.008~0.015cm 3 / g, or 0.004~0.011cm 3 / g, more specifically, for example, 0.004 cm 3 / g, 0.005cm 3 / g, 0.006cm 3 / g, 0.007cm 3 / g, 0.008cm 3 / g, 0.009cm 3 / g, 0.010cm 3 / g, 0.011cm 3 / g, 0.012cm 3 / g, 0.013cm3 / g, 0.014cm 3 / g, 0.015cm 3 / g; the overall pore volume of cobalt trioxide is 0.002~0.080cm 3 / g, for example, 0.002 to 0.004 cm 3 / g, or 0.004~0.006cm 3 / g, or 0.006~0.009cm 3 / g, or 0.009~0.01cm 3 / g, or 0.01~0.05cm 3 / g, or 0.05~0.08cm 3 / g, or 0.003~0.015cm 3 / g, more specifically, it can be 0.002cm 3 / g, 0.003cm 3 / g, 0.004cm 3 / g, 0.005cm 3 / g, 0.006cm 3 / g, 0.007cm 3 / g, 0.008cm 3 / g, 0.009cm 3 / g, 0.010cm 3 / g, 0.011cm 3 / g, 0.012cm 3 / g, 0.013cm 3 / g, 0.014cm 3 / g, 0.015cm 3 / g, 0.016cm 3 / g, 0.017cm 3 / g, 0.018cm 3 / g, 0.019cm 3 / g, 0.020cm 3 / g, 0.025cm 3 / g, 0.030cm 3 / g, 0.035cm 3 / g, 0.040cm 3 / g, 0.045cm 3 / g, 0.050cm 3 / g, 0.055cm 3 / g, 0.060cm 3 / g, 0.065cm 3 / g, 0.070cm 3 / g, 0.075cm3 / g or 0.080cm 3 / g;

[0040] The porosity and pore volume of cobalt carbonate and cobalt oxide in this disclosure are tested using a fully automatic specific surface area and pore size distribution tester (model: BELPREP-VACII / BELSORP-MINI-X) produced by American Mychik Co., Ltd. The test principle is nitrogen adsorption method. The specific test method is operated with reference to the instrument operating procedures and built-in workstation software provided by the manufacturer. The test results are different from the method of using Avizo and other software to calculate the ratio of pore area to total area in the cross-sectional photograph. Among them, the porosity and pore volume of the core layer of cobalt oxide are tested after the cobalt carbonate core layer sample is sintered into a cobalt oxide core layer.

[0041] O. The D50 of cobalt trioxide is 5.5 to 23.0 μm, for example, 5.5 to 10.0 μm, or 10.0 to 12.0 μm, or 12.0 to 15.0 μm, or 15.0 to 16.0 μm, or 16.0 to 17.0 μm, or 17.0 to 20.0 μm, or 20.0 to 23.0 μm, or 14.0 to 17.0 μm, and more specifically, for example, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm m, 10.0μm, 10.5μm, 11.0μm, 11.5μm, 12.0μm, 12.5μm, 13.0μm, 13.5μm, 14.0μm, 14.5μm, 15.0μm, 15.5μm, 16.0μm, 16 .5μm, 17.0μm, 17.5μm, 18.0μm, 18.5μm, 19.0μm, 19.5μm, 20.0μm, 20.5μm, 21.0μm, 21.5μm, 22.0μm, 22.5μm or 23.0μm;

[0042] P. The tap density of cobalt tetroxide is 2.0~3.0g / cm 3 , for example, it can be 2.0 to 2.3 g / cm 3 , or 2.3~2.5g / cm 3 , or 2.5~2.6g / cm 3 , or 2.6~2.8g / cm 3 , or 2.8~3.0g / cm 3 , or 2.4~3.0g / cm 3 , more specifically, it can be 2.0 g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3, 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 or 3.0g / cm 3 ;

[0043] Q. The specific surface area of ​​cobalt tetroxide is 2.0 to 15 m 2 / g, for example, 2.0 to 4.0 m 2 / g, or 4.0~6.0m 2 / g, or 6.0~10.0m 2 / g, or 10-15m 2 / g, or 3.0~4.5m 2 / g, more specifically, for example, 2.0m 2 / g, 3.0m 2 / g, 4.0m 2 / g, 5.0m 2 / g, 6.0m 2 / g, 7.0m 2 / g, 8.0m 2 / g, 9.0m 2 / g, 10.0m 2 / g, 11.0m 2 / g, 12.0m 2 / g, 13.0m 2 / g, 14.0m 2 / g or 15.0m 2 / g.

[0044] A second aspect of the present disclosure further provides a cobalt carbonate comprising a core layer and a coating layer coated outside the core layer, as shown in FIG40 ; the core layer and the coating layer are both doped with Al, and the Al doping content of the core layer is higher than the Al doping content of the coating layer;

[0045] The cobalt carbonate provided by the present disclosure includes a core layer and a coating layer coated outside the core layer. By gradient-doping the cobalt carbonate particles as a whole with Al, and with a higher Al doping amount in the core layer than in the coating layer, the crystal structure stability of the LCO material after sintering can be improved, thereby improving the cycle performance. For cobalt carbonate, the Al element exists in the form of amorphous aluminum hydroxide during the crystallization process. The lower aluminum content in the coating layer is conducive to controlling the hydrolysis of amorphous aluminum hydroxide during centrifugal washing; and the porosity and pore volume of the coating layer are lower than those of the core layer, which is conducive to inhibiting the hydrolysis of amorphous aluminum hydroxide in the core layer, thereby improving the uniformity of aluminum element distribution.

[0046] Preferably, the cobalt content of the cobalt carbonate decreases layer by layer from the core layer to the coating layer.

[0047] The cobalt carbonate coating is a functional layer. By increasing the doping element content in each layer, the specific performance effects of the sintered cathode material are enhanced, improving the overall performance of the sintered LCO. The cobalt content in the product decreases layer by layer from the inside out, reducing the surface Co content, lowering Co dissolution, and improving safety performance.

[0048] Preferably, the cobalt carbonate satisfies at least one of the following conditions a to l:

[0049] a. The coating layer of cobalt carbonate is 1 to 5 layers, for example, 1 layer, 2 layers, 3 layers, 4 layers or 5 layers;

[0050] b. The ratio of the mass of doped Al in the core layer of cobalt carbonate to the total mass of metal in the core layer of cobalt carbonate is: 0.26 to 0.80wt%, for example, 0.26 to 0.30wt%, or 0.30 to 0.40wt%, or 0.40 to 0.50wt%, or 0.50 to 0.70wt%, or 0.70 to 0.80wt%, more specifically, for example, 0.26wt%, 0.30wt%, 0.35wt%, 0.40wt%, 0.50wt%, 0.60wt%, 0.70wt% or 0.80wt%;

[0051] c. The ratio of the mass of doped Al in the cobalt carbonate coating to the total mass of the metal in the cobalt carbonate is: 0.01 to 0.27 wt %, for example, 0.01 to 0.04 wt %, or 0.04 to 0.1 wt %, or 0.05 to 0.15 wt %, or 0.15 to 0.27 wt %, more specifically, for example, 0.01 wt %, 0.02 wt %, 0.05 wt %, 0.08 wt %, 0.1 wt %, 0.15 wt %, 0.2 wt %, 0.25 wt % or 0.27 wt %;

[0052] The test method for the ratio of the mass of doped Al in the cobalt carbonate coating layer to the total metal mass in the cobalt carbonate involved in the present application is: respectively determine the mass fraction of the mass of Al in the cobalt carbonate core layer and the cobalt carbonate in the total metal mass, and then subtract the mass fraction of the mass of Al in the cobalt carbonate core layer from the mass fraction of the mass of Al in the cobalt carbonate core layer in the total metal mass to obtain the difference, which is the metal mass ratio of the doped element Al in the cobalt carbonate coating layer to the cobalt carbonate.

[0053] d. When the cobalt carbonate coating layer is 1 layer, the molar ratio of cobalt in the cobalt carbonate coating layer to the total molar amount of metal in the cobalt oxide coating layer is ≤70 mol%, for example, 50 mol%, 55 mol%, 60 mol%, 65 mol%, 67 mol%, 69 mol% or 70 mol%;

[0054] e. When the cobalt carbonate coating layer is 2 to 5 layers, the molar amount of cobalt in the outermost layer of the cobalt carbonate coating layer to the total molar amount of cobalt carbonate coating layer is ≤70mol%, for example, 50mol%, 55mol%, 60mol%, 65mol%, 67mol%, 69mol% or 70mol%;

[0055] f. The diameter of the core layer of cobalt carbonate is 8.0 to 23.0 μm, for example, 8.0 to 10.0 μm, or 10.0 to 13.0 μm, or 13.0 to 18.0 μm, 18.0 to 23.0 μm, or 18.0 to 21.0 μm; more specifically, for example, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0 or 23.0 μm;

[0056] g. When the coating layer of cobalt carbonate is one layer, the coating layer thickness is 0.15 to 1.5 μm, preferably, the coating layer thickness is 0.15 to 0.5 μm; for example, it can be 0.15 to 0.30 μm, or 0.30 to 0.40 μm, or 0.40 to 0.50 μm, or 0.50 to 0.70 μm, or 0.70 to 1.0 μm, or 1.0 to 1.5 μm, more specifically, for example, it can be 0.15 μm, 0.20 μm, 0.25 μm, 0.30 μm, 0 .35μm, 0.40μm, 0.45μm, 0.50μm, 0.55μm, 0.60μm, 0.65μm, 0.70μm, 0.75μm, 0.80μm, 0.85μm, 0.90μm, 0.9 5μm, 1.0μm, 1.05μm, 1.10μm, 1.15μm, 1.20μm, 1.25μm, 1.30μm, 1.30μm, 1.35μm, 1.40μm, 1.45μm or 1.5μm;

[0057] h. When the coating layer of cobalt carbonate is 2 to 5 layers, the thickness of the single layer in the coating layer is 0.15 to 1.5 μm. Preferably, the thickness of the single layer of the coating layer is 0.15 to 0.5 μm; for example, it can be 0.15 to 0.30 μm, or 0.30 to 0.40 μm, or 0.40 to 0.50 μm, or 0.50 to 0.70 μm, or 0.70 to 1.0 μm, or 1.0 to 1.5 μm, or 0.2 to 0.5 μm, and more specifically, it can be 0.15 μm, 0.20 μm, or 0.25 μm. , 0.30μm, 0.35μm, 0.40μm, 0.45μm, 0.50μm, 0.55μm, 0.60μm, 0.65μm, 0.70μm, 0.75μm, 0.80μm, 0.85μm, 0.90μ m, 0.95μm, 1.0μm, 1.05μm, 1.10μm, 1.15μm, 1.20μm, 1.25μm, 1.30μm, 1.30μm, 1.35μm, 1.40μm, 1.45μm or 1.5μm;

[0058] i. The core layer of cobalt carbonate also includes Ni and / or Mn;

[0059] j. When condition i is met, the ratio of the mass of Ni and Mn doped in the core layer of cobalt carbonate to the total mass of the metal in the core layer of cobalt carbonate is independently: 0.07 to 2.00 wt%, for example, 0.07 to 0.10 wt%, or 0.10 to 0.30 wt%, or 0.30 to 1.50 wt%, or 0.50 to 1.00 wt%, or 1.00 to 2.00 wt%, more specifically, for example, 0.07 wt%, 0.10 wt%, 0.50 wt%, 0.8 wt%, 1.00 wt%, 1.20 wt%, 1.30 wt%, 1.40 wt%, 1.50 wt%, 1.60 wt%, 1.70 wt%, 1.80 wt%, 1.90 wt% or 2.00 wt%;

[0060] k. The cobalt carbonate coating layer further includes one or more doping elements selected from the group consisting of Mg, Ti, La, Zr, Y, Ca, Sr, and Ba; that is, the cobalt carbonate coating layer may be doped with one or more of the aforementioned elements in addition to Al; more specifically, when the cobalt carbonate coating layer is a single layer, it may be doped with one or more of the aforementioned elements in addition to Al; and when the cobalt carbonate coating layer is a multi-layer layer, each layer may be doped with only one of the aforementioned elements in addition to Al, or each layer may be doped with multiple of the aforementioned elements in addition to Al.

[0061] Preferably, when the coating layer is two layers, the coating layer is divided into an inner layer and an outer layer, the inner layer of the coating layer further includes one or more of Zr, La, Ca, Ba, Y, Ti, and Sr; the outer layer of the coating layer further includes one or more of Mg, Zr, Ti, and Sr;

[0062] When the coating layer has 3-5 layers, the coating layer is divided into an inner layer, an intermediate layer and an outer layer, the inner layer and the outer layer are respectively 1 layer, and all layers other than the inner layer and the outer layer are intermediate layers. The inner layer of the coating layer further includes one or more of Zr, La, Ca, and Ba; the intermediate layer of the coating layer further includes one or more of La, Zr, Y, Ti, and Sr; and the outer layer of the coating layer further includes one or more of Mg, Zr, Ti, and Sr;

[0063] l. When condition k is met, the ratio of the mass of the other doping elements in the coating layer of cobalt carbonate except Al to the total metal mass in cobalt carbonate is independently: 0.01-0.30wt%, for example, 0.01-0.15wt%, or 0.15-0.30wt%, or 0.04-0.12wt%, or 0.02-0.14wt%, more specifically, for example, 0.01wt%, 0.02wt%, 0.03wt%, 0.04wt%. %, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.10wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt% , 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt%, 0.20wt%, 0.22wt%, 0.24wt%, 0.28wt%, 0.30wt%.

[0064] The test method for the ratio of the mass of other doping elements in the coating layer of cobalt carbonate except Al to the total metal mass in cobalt carbonate involved in this application is: dividing the measured mass fraction of other doping elements in cobalt carbonate except Al by the total metal mass fraction in cobalt carbonate, that is, the ratio of the mass of other doping elements in the coating layer of cobalt carbonate except Al to the total metal mass in cobalt carbonate.

[0065] Preferably, the cobalt carbonate satisfies at least one of the following conditions m to q:

[0066] m. The porosity of the core layer of cobalt carbonate is 15 to 25%, for example, 15% to 17%, or 17% to 18%, or 18% to 20%, or 21% to 23%, or 23% to 25%, more specifically, for example, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%, and the overall porosity of cobalt carbonate is 14 to 25%, for example, 14% to 17%, or 17% to 20%, or 20% to 25%, or 20% to 23%, or 23% to 24%, or 24% to 25%, or 23% to 25%, more specifically, for example, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%;

[0067] n. The pore volume of the core layer of cobalt carbonate is 0.08~0.30cm 3 / g, for example, 0.08 to 0.12 cm 3 / g, or 0.12~0.16cm 3 / g, or 0.16~0.20cm 3 / g, or 0.20~0.25cm 3 / g, or 0.25~0.30cm 3 / g, or 0.10~0.15cm 3 / g, more specifically, it can be 0.08cm 3 / g, 0.09cm 3 / g, 0.10cm 3 / g, 0.11cm 3 / g, 0.12cm 3 / g, 0.13cm 3 / g, 0.14cm 3 / g, 0.15cm 3 / g, 0.16cm 3 / g, 0.17cm 3 / g, 0.18cm 3 / g, 0.19cm 3 / g, 0.20cm 3 / g, 0.21cm 3 / g, 0.22cm 3 / g, 0.23cm 3 / g, 0.24cm 3 / g, 0.25cm 3 / g, 0.26cm 3 / g, 0.27cm 3 / g, 0.28cm 3 / g, 0.29cm 3 / g or 0.30cm3 / g; the overall pore volume of cobalt carbonate is 0.05~0.25cm 3 / g, for example, 0.05 to 0.08 cm 3 / g, or 0.08~0.10cm 3 / g, or 0.10~0.16cm 3 / g, or 0.10~0.13cm 3 / g, or 0.13~0.16cm 3 / g, or 0.16~0.20cm 3 / g, or 0.20~0.25cm 3 / g, or 0.10~0.17cm 3 / g, more specifically, it can be 0.05cm 3 / g, 0.06cm 3 / g, 0.07cm 3 / g, 0.08cm 3 / g, 0.09cm 3 / g, 0.10cm 3 / g, 0.11cm 3 / g, 0.12cm 3 / g, 0.13cm 3 / g, 0.14cm 3 / g, 0.15cm 3 / g, 0.16cm 3 / g, 0.17cm 3 / g, 0.18cm 3 / g, 0.19cm 3 / g, 0.20cm 3 / g, 0.21cm 3 / g, 0.22cm 3 / g, 0.23cm 3 / g, 0.24cm 3 / g or 0.25cm 3 / g;

[0068] o. The D50 of cobalt carbonate is 8.7 to 30.0 μm, for example, 8.7 to 12.0 μm, or 12.0 to 15.0 μm, or 15.0 to 17.0 μm, or 17.0 to 19.0 μm, or 19.0 to 23.0 μm, or 19.0 to 20.0 μm, or 20.0 to 21.0 μm, or 21.0 to 22.0 μm, or 23. 0 to 30.0 μm, more specifically, for example, 8.7, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0, 23.0, 24.0, 25.0, 26.0, 27.0, 28.0, 29.0 or 30.0 μm;

[0069] p. The specific surface area of ​​cobalt carbonate is 50 to 150 m 2 / g, for example, 50 to 70 m 2 / g, or 70-90m 2 / g, or 90-100m 2 / g, or 100-110m 2 / g, or 110-120m 2 / g, or 120-150m 2 / g, or 85-130m 2 / g, more specifically, it can be 85m 2 / g、90m 2 / g、95m 2 / g、100m 2 / g、105m 2 / g、110m 2 / g, 115m 2 / g, 120m 2 / g、125m 2 / g, 130m 2 / g、135m 2 / g, 140m 2 / g、145m 2 / g or 150m 2 / g;

[0070] q. The tap density of cobalt carbonate is 1.5-2.0 g / cm 3 , for example, it can be 1.5 to 1.6 g / cm 3 , or 1.6~1.7g / cm 3 , or 1.7~1.8g / cm 3 , or 1.8~1.9g / cm 3 , or 1.9~2.0g / cm 3 , or 1.6~1.8g / cm3 , for example, 1.60m 2 / g, 1.65m 2 / g, 1.70m 2 / g, 1.75m 2 / g, 1.80m 2 / g, 1.85m 2 / g, 1.90m 2 / g, 1.95m 2 / g or 2.0m 2 / g.

[0071] The third aspect of the present disclosure further provides a method for preparing cobalt carbonate, comprising:

[0072] The core layer cobalt salt solution and the precipitant solution are added to a reactor containing a base liquid to react, the flow rate of the core layer cobalt salt solution increases with the increase of the material particle size, the flow rate of the precipitant solution increases with the increase of the flow rate of the core layer cobalt salt solution, and the stirring speed of the reactor decreases with the increase of the material particle size. The reaction is continued until the particle size D50 is 8.0 to 23.0 μm, thereby obtaining a cobalt carbonate core layer;

[0073] The coating layer cobalt salt solution and the precipitant solution are sequentially added into a reactor containing a cobalt carbonate core layer to react until the growth of each coating layer is completed to obtain cobalt carbonate.

[0074] The diameter particle size D50 of the cobalt carbonate core layer obtained by the reaction is 8.0-23.0 μm, for example, 8.0-10.0 μm, or 10.0-13.0 μm, or 13.0-18.0 μm, 18.0-23.0 μm, or 18.0-21.0 μm; more specifically, for example, it can be 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0 or 23.0 μm;

[0075] The material is a growing cobalt carbonate core layer;

[0076] The core layer cobalt salt solution and the coating layer cobalt salt solution both contain Co and Al. The core layer cobalt salt solution may further contain Ni and / or Mn. The coating layer cobalt salt solution may further contain one or more elements selected from the group consisting of Mg, Ti, La, Zr, Y, Ca, Sr, and Ba.

[0077] Wherein, the cobalt salt is selected from one or more of cobalt sulfate, cobalt chloride, and cobalt nitrate; the precipitant is selected from one or more of ammonium bicarbonate, ammonium carbonate, and sodium carbonate; and the base liquid is selected from one or more of ammonium bicarbonate, ammonium carbonate, and sodium carbonate;

[0078] The cobalt concentration in the cobalt salt solution is 85-125 g / L.

[0079] Specifically, the cobalt concentration in the core layer cobalt salt solution is 85 to 125 g / L, for example, 90 to 110 g / L, or 80 to 100 g / L, 100 to 125 g / L, more specifically, for example, 85 g / L, 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L or 125 g / L;

[0080] The cobalt concentration in the coating layer cobalt salt solution is 85-125 g / L, for example, 90-110 g / L, or 80-100 g / L, 100-125 g / L, more specifically, for example, 85 g / L, 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L or 125 g / L;

[0081] The concentration of the precipitant solution is 180-220 g / L, for example, 180-200 g / L, or 180-190 g / L, or 190-200 g / L, or 200-210 g / L, more specifically, for example, 180 g / L, 185 g / L, 190 g / L, 195 g / L, 200 g / L, 205 g / L, 210 g / L, 215 g / L, or 220 g / L; the pH of the base solution is 7.5-8.8, for example, 7.5-8.0, or 8.0-8.8, 7.8-8.8, or 7.8-8.6, more specifically, for example, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, or 8.8;

[0082] The pH value during the reaction of preparing the cobalt carbonate core layer is 7.0-8.3, and the ammonium concentration is 10-60 g / L; the ammonium concentration is NH4 + Concentration, the same below;

[0083] More specifically, for example, the pH during the reaction process for preparing the cobalt carbonate core layer can be 7.0-7.6, or 7.6-8.0, or 8.0-8.4, and more specifically, can be 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2 or 8.3; the ammonium concentration can be 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L, 50 g / L, 55 g / L, 60 g / L, or 10-40 g / L, or 30-60 g / L;

[0084] The pH during the reaction for preparing the cobalt carbonate coating layer is 6.5-8.0, and the ammonium concentration is 10-40 g / L;

[0085] More specifically, for example, the pH during the reaction for preparing the cobalt carbonate coating layer may be 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, or 6.7-7.5, or 7.5-8.0; the ammonium concentration may be 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, or 10-27 g / L, or 20-35 g / L, or 25-40 g / L;

[0086] The flow rate of the core layer cobalt salt solution is 1.5% / h-7.0% / h of the available volume of the reactor, and more specifically, for example, it can be 1.5% / h, 2.0% / h, 2.5% / h, 3.0% / h, 3.5% / h, 4.0% / h, 4.5% / h, 5.0% / h, 5.5% / h, 6.0% / h, 6.5% / h or 7.0% / h; the flow rate of the coating layer cobalt salt solution is 1.5% / h-3.5% / h of the available volume of the reactor, and more specifically, for example, it can be 1.5% / h, 2.0% / h, 2.5% / h, 3.0% / h or 3.5% / h.

[0087] The fourth aspect of the present disclosure further provides a method for preparing cobalt tetroxide, which is obtained by sintering the above-mentioned cobalt carbonate.

[0088] The fifth aspect of the present disclosure further provides a positive electrode material, which is lithium cobalt oxide obtained by calcining the above-mentioned cobalt trioxide and a lithium source;

[0089] Preferably, the molar ratio of the lithium source to the cobalt oxide is (1-1.05):1, more specifically, for example, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1 or 1.05:1;

[0090] Preferably, the calcination temperature is 900°C to 1200°C, more specifically, for example, it can be 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C or 1200°C; the calcination time is 20 to 30h, more specifically, for example, it can be 20h, 22h, 24h, 26h, 28h or 30h.

[0091] The sixth aspect of the present disclosure further provides a lithium-ion battery, the raw materials of which include the above-mentioned positive electrode material.

[0092] Compared with the prior art, the advantages of the present invention include:

[0093] 1. The cobalt carbonate and the corresponding cobalt oxide provided by the present disclosure include a core layer and a coating layer coated outside the core layer. By doping the cobalt carbonate and the corresponding cobalt oxide particles with Al as a whole, and with the Al doping amount of the core layer being higher than that of the coating layer, the crystal structure stability of the LCO material after sintering can be improved, thereby improving the cycle performance. For cobalt carbonate, the Al element exists in the form of amorphous aluminum hydroxide during the crystallization process. The lower aluminum content in the coating layer is conducive to controlling the hydrolysis of amorphous aluminum hydroxide during centrifugal washing; and the porosity and pore volume of the coating layer are lower than those of the core layer, which is conducive to inhibiting the hydrolysis of amorphous aluminum hydroxide in the core layer, thereby improving the uniformity of aluminum element distribution.

[0094] 2. The volume proportion of the cobalt carbonate and cobalt oxide core layer provided by the present invention is extremely large, and Ni and Mn elements are further doped to improve the core functions of long endurance and cycle life that are of general concern in the industry. When synthesizing cobalt carbonate, the Ksp values ​​(solubility product constants) of Ni and Co elements are relatively similar, which can be better co-precipitated to improve uniformity. In cobalt carbonate and cobalt oxide, Ni replaces part of Co in the crystal lattice, which can improve capacity performance; doping with Mn and Ni can also convert the phase change into solid solution behavior, effectively inhibiting the O3 / H1-3 phase change of the sintered LCO material at a voltage of 4.5V, inhibiting crystal expansion, improving the stability of the crystal structure, increasing the platform voltage, and improving the cycle performance. If the volume proportion of the core layer is too small, the improvement in cycle and capacity will not be obvious.

[0095] 3. The cobalt carbonate and cobalt oxide coating layers provided by the present invention are coated on the outside of the core layer. The coating layer is very thin and accounts for a small proportion. The coating layer can be modified according to the customized needs of the customer to achieve the differentiated needs of different customers. Specifically, by setting the number of coating layers and different doping elements in each layer, each coating layer can achieve its specific function. For example, La, Zr and other elements are added to the coating layer, which have a large ionic radius to form a lithium garnet (LLZO) solid phase layer, so that the LCO material has good ion mobility and electrochemical stability; doping with Y and Ti can stabilize the structure, inhibit phase change, and improve rate performance; Mg doping can form a continuous channel, improve ion transmission efficiency, and improve surface conductivity; doping with Sr can improve conductivity, reduce impedance, and improve stability; doping with Ca can stabilize the material skeleton structure; doping with Ba can enhance the structural stability of lithium cobalt oxide, etc. Because the volume of the coating layer accounts for a small proportion, it is necessary to increase the content of doping elements to improve the material-specific performance effect and improve the overall performance of LCO.

[0096] 4. The present invention controls the cobalt content in the core layer cobalt solution and the coating layer cobalt solution during the preparation of cobalt carbonate, thereby controlling the cobalt content in cobalt carbonate and cobalt tetroxide, so that the cobalt content in the product decreases layer by layer from the inside to the outside, thereby reducing the surface Co 4+ content, reduce Co dissolution and improve safety performance.

[0097] 5. In the present disclosure, the more types of doping elements and the higher the doping amount of cobalt carbonate and cobalt tetroxide, the more difficult it is to uniformly dope the doping elements. The present disclosure improves the product structure design and preparation method of cobalt carbonate and cobalt tetroxide, separates the doping elements of the core layer and the coating layer according to the different functions to be achieved, and each layer of the coating layer has different types of doping elements. The coating layer is designed to be very thin, which can minimize the problem of reduced capacity and cycle performance of the final LCO material due to uneven doping.

[0098] 6. In the present disclosure, when preparing cobalt carbonate, the flow rate of the core layer cobalt salt solution is controlled to increase with the increase of the material particle size, the flow rate of the precipitant solution is controlled to increase with the increase of the flow rate of the core layer cobalt salt solution, and the stirring speed of the reactor is controlled to decrease with the increase of the material particle size. The obtained cobalt carbonate particles, cobalt tetroxide, and lithium cobaltate have moderate overall porosity, specific surface area, and overall pore volume, good doping uniformity, and the corresponding lithium ion battery has a high cycle retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0099] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope of the present disclosure.

[0100] FIG1 is a scanning electron microscope morphology result of the core layer of the cobalt carbonate particles of Example 1;

[0101] FIG2 is a scanning electron microscope morphology result of the cobalt carbonate particle coating layer of Example 1;

[0102] FIG3 is a scanning electron microscope morphology result of a cross section of the coating layer of the cobalt carbonate particles of Example 1;

[0103] FIG4 is a scanning electron microscope morphology result of cobalt trioxide of Example 1;

[0104] FIG5 is a scanning electron microscope morphology result of a cross section of cobalt tetroxide in Example 1;

[0105] 6 and 7 are respectively the analysis results of Al and Ni components in the core layer micro-region of cobalt tetroxide in Example 1;

[0106] 8 to 10 are respectively the analysis results of Zr, Y, and Ti components of the cobalt oxide coating micro-region of Example 1;

[0107] FIG11 is a scanning electron microscope morphology result of the cobalt carbonate particles of Example 2;

[0108] FIG12 is a scanning electron microscope morphology image of a cross section of cobalt carbonate particles of Example 2;

[0109] FIG13 is a scanning electron microscope morphology result of cobalt trioxide of Example 2;

[0110] FIG14 is a scanning electron microscope morphology result of a cross section of cobalt tetroxide in Example 2;

[0111] FIG15 is a diagram showing the Al composition analysis results of the core layer microregion of cobalt tetroxide in Example 2;

[0112] 16 and 17 are respectively the Zr and Ti composition analysis results of the cobalt oxide coating micro-region of Example 2;

[0113] FIG18 is a scanning electron microscope morphology image of the cobalt carbonate particles of Example 3;

[0114] FIG19 is a scanning electron microscope morphology result of cobalt trioxide of Example 3;

[0115] FIG20 is a scanning electron microscope morphology result of a cross section of cobalt tetroxide in Example 3;

[0116] FIG21 is a scanning electron microscope morphology image of the cobalt carbonate particles of Example 4;

[0117] FIG22 is a scanning electron microscope morphology result of cobalt trioxide of Example 4;

[0118] FIG23 is a scanning electron microscope morphology result of a cross section of cobalt tetroxide in Example 4;

[0119] FIG24 is a scanning electron microscope morphology image of the cobalt carbonate particles of Example 5;

[0120] FIG25 is a scanning electron microscope morphology result of cobalt trioxide of Example 5;

[0121] FIG26 is a scanning electron microscope morphology image of the cobalt carbonate particles of Example 6;

[0122] FIG27 is a scanning electron microscope morphology result of cobalt trioxide of Example 6;

[0123] FIG28 is a scanning electron microscope morphology image of the cobalt carbonate particles of Example 7;

[0124] FIG29 is a scanning electron microscope morphology image of cobalt trioxide of Example 7;

[0125] FIG30 is a scanning electron microscope morphology image of the cobalt carbonate particles of Example 8;

[0126] FIG31 is a scanning electron microscope morphology result of cobalt trioxide of Example 8;

[0127] FIG32 is a scanning electron microscope morphology result of the cobalt carbonate particles of Comparative Example 1;

[0128] FIG33 is a scanning electron microscope morphology result of cobalt trioxide of Comparative Example 1;

[0129] FIG34 is a scanning electron microscope morphology result of a cross section of cobalt tetroxide in Comparative Example 1;

[0130] FIG35 is a scanning electron microscope morphology result of the cobalt carbonate particles of Comparative Example 2;

[0131] FIG36 is a scanning electron microscope morphology result of a cross section of the cobalt carbonate particles of Comparative Example 2;

[0132] FIG37 is a scanning electron microscope morphology result of cobalt trioxide of Comparative Example 2;

[0133] FIG38 is a scanning electron microscope morphology result of a cross section of cobalt tetroxide in Comparative Example 2;

[0134] FIG39 is a diagram showing the Al composition analysis results of the cobalt oxide coating layer micro-area of ​​Comparative Example 2;

[0135] FIG40 is a schematic diagram of the structures of cobalt carbonate and cobalt trioxide disclosed in the present invention;

[0136] FIG41 is a schematic diagram of the structures of cobalt carbonate and cobalt trioxide in Example 1. DETAILED DESCRIPTION

[0137] As used herein:

[0138] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0139] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0140] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0141] The embodiments of the present disclosure will be described in detail below with reference to specific examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer were used. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0142] Example 1

[0143] Example 1 provides a cobalt tetroxide precursor having a core layer doped with Al: 0.85wt% and Ni: 1.2wt% and a coating layer consisting of 5 layers, wherein the molar ratio of the doping elements in each coating layer is close to the molar ratio of the doping elements in the cobalt liquid of the coating layer during preparation, and are approximately n1: Co:Al:Zr = 0.95:0.03:0.02, n2: Co:Al:La = 0.94:0.03:0.03, n3: Co:Al:Y = 0.91:0.03:0.06, n4: Co:Al:Ti = 0.88:0.03:0.09, n5: Co:Al:Mg = 0.67:0.03:0.30, and its structural schematic diagram is shown in Figure 41. Among them, n1 is the first coating layer coated outside the core layer, n2 is the second coating layer coated outside the first coating layer, n3 is the third coating layer coated outside the second coating layer, n4 is the fourth coating layer coated outside the third coating layer, n5 is the fifth coating layer coated outside the fourth coating layer, and the same below.

[0144] The preparation process is as follows:

[0145] 1. Nickel sulfate, aluminum sulfate, and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with nickel and aluminum elements, which serves as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt, nickel, and aluminum elements in the solution is Co:Ni:Al=1:0.017:0.026; the concentration of the coating layer cobalt salt solution is mixed according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 190 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 is prepared as a base solution.

[0146] 2. The prepared core layer cobalt salt solution and precipitant solution are simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the cobalt salt solution is gradually increased from 2.5% / h to 6.0% / h of the available volume of the reactor, the flow rate of the precipitant solution is twice the flow rate of the cobalt salt solution, and the stirring speed is gradually reduced from 350 r / min to 150 r / min. During the reaction, the pH value is controlled at 7.0-7.4 and the ammonium concentration is controlled at 15-30 g / L until the particle size D50 grows to 20.5 μm, thereby obtaining a cobalt carbonate core layer.

[0147] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.5% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.5 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in according to the coating layer sequence. The thickness of each coating layer was about 0.25 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 6.8-7.2, and the ammonium concentration was controlled at 10-25 g / L until the aluminum-doped cobalt carbonate of Example 1 was prepared.

[0148] The surface scanning electron microscopy morphology of the core layer of the cobalt carbonate secondary particles of Example 1 is shown in Figure 1, the surface scanning electron microscopy morphology of the coating layer of the cobalt carbonate secondary particles is shown in Figure 2, and the scanning electron microscopy morphology of the cross-section is shown in Figure 3. The right image in Figure 3 is an enlarged view of the left image. The morphologies of the core layer microregion and the coating layer microregion are different, and the coating layer has a ring-shaped structure with alternating density and sparseness, indicating a multilayer structure.

[0149] The cobalt carbonate core layer and cobalt carbonate prepared in Example 1 were sampled.

[0150] Test method for the mass fraction of cobalt in the sample: refer to "GB / T 23367.1-2009 Chemical analysis method of lithium cobaltate Part 1: Determination of cobalt content EDTA titration method". Test method for the mass fraction of each metal element other than cobalt in the sample: refer to "GB / T 23367.2-2009 Chemical analysis method of lithium cobaltate Part 2: Determination of lithium, nickel, manganese, magnesium, aluminum, iron, sodium, calcium and copper content inductively coupled plasma atomic emission spectrometry". The instrument is the ICP spectrometer Avio500. Some doping elements La, Zr, Y, and Ti involved in this application that are not within the standard range are prepared with standard solutions referring to the doping element Ni and tested. The test data are as follows:

[0151] ① The mass ratio of each doping element in the cobalt carbonate core layer of Example 1 to the mass ratio of cobalt carbonate (i.e. the doping elements and contents of the core layer in Table 1) are: Al 0.56wt%, Ni 0.80wt%,

[0152] ② The mass ratios of the doping elements in the cobalt carbonate of Example 1 to the mass ratio of the cobalt carbonate are: Al: 0.605wt%, Zr: 0.026wt%, La: 0.05wt%, Y: 0.08wt%, Ti: 0.06wt%, Mg: 0.13wt%.

[0153] Since the cobalt carbonate core layer does not contain doping elements Zr, La, Y, Ti, and Mg, the mass ratio of the doping elements Zr, La, Y, Ti, and Mg in the cobalt carbonate mass ratio (i.e., the mass ratio of the doping elements in the coating layer to the cobalt carbonate mass ratio in Table 1) are Zr: 0.026wt%, La: 0.05wt%, Y: 0.08wt%, Ti: 0.06wt%, and Mg: 0.13wt%, respectively;

[0154] In cobalt carbonate, since the coating layer is very thin, the mass of the coating layer accounts for a very small proportion of the mass of the entire cobalt carbonate. The mass of the coating layer is ignored, and the mass of the core layer is assumed to be the mass of the entire cobalt carbonate; then:

[0155] It can be obtained that: the mass ratio of Al in the coating layer to the mass ratio of cobalt carbonate ≈ the mass ratio of Al in cobalt carbonate to the mass ratio of cobalt carbonate - the mass ratio of Al in the core layer to the mass ratio of the core layer = 0.605% - 0.56% = 0.045%.

[0156] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 840° C., a sintering time of 2.5 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 3.5 cm to prepare the multinary doped cobalt tetroxide of Example 1.

[0157] The schematic diagram of the structure of cobalt carbonate and cobalt oxide in Example 1 is shown in Figure 41, the scanning electron microscope morphology of the surface cobalt oxide secondary particles of Example 1 is shown in Figure 4, and the scanning electron microscope morphology of the cross-section is shown in Figure 5. Among them, the right figure of Figure 5 is an enlarged view of the left figure. The morphologies of the core layer microregion and the coating layer microregion are different, and the coating layer has a ring-shaped sparse and dense alternating structure, which is a multi-layer structure. The cobalt oxide in Example 1 was analyzed for Al and Ni components in the cross-section microregion of the core layer using an electron probe instrument. The results are shown in Figures 6 and 7 respectively. The Ni and Al elements are evenly distributed. The cobalt oxide in Example 1 was analyzed for Zr, Y, and Ti components in the cross-section coating layer microregion of the secondary particles using an electron probe instrument. The results are shown in Figures 8 to 10 respectively. Each doping element is evenly distributed in the doped coating layer monolayer.

[0158] The cobalt carbonate core layer and cobalt carbonate sampled in Example 1 were sintered to obtain the cobalt tetroxide core layer and cobalt tetroxide sample. The test method for the mass fraction of cobalt in the sample: refer to "GB / T 23367.1-2009 Chemical analysis method of lithium cobaltate Part 1: Determination of cobalt content EDTA titration method". The test method for the mass fraction of each metal element other than cobalt in the sample: refer to "GB / T 23367.2-2009 Chemical analysis method of lithium cobaltate Part 2: Determination of lithium, nickel, manganese, magnesium, aluminum, iron, sodium, calcium and copper content Inductively coupled plasma atomic emission spectrometry". The instrument is ICP spectrometer Avio500. The doping elements La, Zr, Y, and Ti involved in this application that are not within the standard range are prepared with reference to the doping element Ni as the standard solution and tested. The data obtained from the test are as follows:

[0159] ③ The mass ratio of each doping element in the cobalt tetroxide core layer of Example 1 to the mass ratio of cobalt tetroxide (i.e. the doping elements and contents of the core layer in Table 2) are: Al 0.85wt%, Ni 1.2wt%,

[0160] ④ The mass ratios of the doping elements in the cobalt tetroxide of Example 1 to the mass ratio of the cobalt tetroxide are: Al: 0.92wt%, Zr: 0.04wt%, La: 0.07wt5%, Y: 0.12wt%, Ti: 0.09wt%, Mg: 0.20wt%.

[0161] Since the cobalt tetroxide core layer does not contain doping elements Zr, La, Y, Ti, and Mg, the mass ratios of the cobalt tetroxide doping elements Zr, La, Y, Ti, and Mg to the mass ratio of cobalt tetroxide (i.e., the mass ratios of the coating layer doping elements to cobalt tetroxide in Table 2) are Zr: 0.04wt%, La: 0.07wt5%, Y: 0.12wt%, Ti: 0.09wt%, and Mg: 0.20wt%, respectively;

[0162] In cobalt tetroxide, since the coating layer is very thin, the mass of the coating layer accounts for a very small proportion of the mass of the entire cobalt tetroxide. Ignoring the mass of the coating layer, the mass of the core layer is assumed to be the mass of the entire cobalt tetroxide; then:

[0163] It can be obtained that: the mass ratio of Al in the coating layer to the mass ratio of cobalt tetroxide ≈ the mass ratio of Al in cobalt tetroxide to the mass ratio of cobalt tetroxide - the mass ratio of Al in the core layer to the mass ratio of the core layer 0.92% - 0.85% = 0.07%.

[0164] 5. The cobalt trioxide obtained in Example 1 and lithium carbonate were uniformly mixed at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 1.

[0165] Example 2

[0166] Example 2 provides a cobalt oxide precursor having a core layer doped with 0.85 wt% Al and 1.2 wt% Mn and 5 coating layers, wherein the molar ratio of the doping elements in each coating layer is close to the molar ratio of the doping elements in the cobalt solution of the coating layer during preparation, namely, n1: Co:Al:La = 0.94:0.03:0.03, n2: Co:Al:Zr = 0.92:0.03:0.04, n3: Co:Al:Y = 0.91:0.03:0.06, n4: Co:Al:Ti = 0.88:0.03:0.09, and n5: Co:Al:Mg = 0.67:0.03:0.30. The preparation process is as follows:

[0167] 1. Aluminum sulfate solution, cobalt sulfate solution, and manganese sulfate solution are mixed to form a cobalt salt solution doped with aluminum and manganese elements, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt and aluminum elements in the solution is: Co:Al:Mn=1:0.026:0.018; the concentration of the coating layer cobalt salt solution is mixed according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 200 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.5 is prepared as a base solution.

[0168] 2. The prepared core layer cobalt salt solution and precipitant solution are simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the core layer cobalt salt solution is gradually increased from 2.7% / h to 6.1% / h of the available volume of the reactor, the flow rate of the precipitant solution is twice the flow rate of the cobalt salt solution, and the stirring speed is gradually reduced from 380 r / min to 160 r / min. During the reaction, the pH value is controlled at 7.1-7.5 and the ammonium concentration is controlled at 18-33 g / L until the particle size D50 grows to 18.5 μm, thereby obtaining a cobalt carbonate core layer.

[0169] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.5% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.5 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in the order of the coating layers. The thickness of each coating layer was about 0.25 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 6.7-7.1, and the ammonium concentration was controlled at 12-25 g / L until the aluminum-doped cobalt carbonate of Example 2 was prepared.

[0170] The surface scanning electron microscopy morphology of the cobalt carbonate secondary particles of Example 2 is shown in FIG11 , and the cross-sectional scanning electron microscopy morphology thereof is shown in FIG12 .

[0171] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 840° C., a sintering time of 2.5 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 3.5 cm to prepare the multinary doped cobalt tetroxide of Example 2.

[0172] The surface scanning electron microscopy morphology of the cobalt oxide secondary particles of Example 2 is shown in Figure 13, and the cross-sectional scanning electron microscopy morphology is shown in Figure 14. The Al composition of the cross-sectional microregion of the core layer of the cobalt oxide of Example 2 was analyzed using an electron microprobe. The results, shown in Figure 15, demonstrate uniform Al distribution. The Zr and Ti compositions of the cross-sectional microregion of the coating layer of the secondary particles of Example 2 were analyzed using an electron microprobe. The results, shown in Figures 16 and 17, demonstrate uniform layer distribution of the doping elements.

[0173] 5. The cobalt trioxide obtained in Example 2 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 2.

[0174] Example 3

[0175] Example 3 provides a cobalt oxide precursor having a core layer doped with 0.95 wt% Al and two coating layers, wherein the molar ratio of the doping elements in each coating layer is close to the molar ratio of the doping elements in the cobalt solution of the coating layer during preparation, namely, n1: Co:Al:La = 0.94:0.03:0.03, and n2: Co:Al:Zr = 0.90:0.03:0.07, respectively. The preparation process is as follows:

[0176] 1. Aluminum sulfate and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with aluminum element, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt and aluminum elements in the solution is: Co:Al = 1:0.029; the concentration of the coating layer cobalt salt solution is mixed and configured according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 200 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.0 is prepared as a base solution.

[0177] 2. The prepared core layer cobalt salt solution and precipitant solution are simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the core layer cobalt salt solution is gradually increased from 2.4% / h to 5.9% / h of the available volume of the reactor, the flow rate of the precipitant solution is twice the flow rate of the cobalt salt solution, and the stirring speed is gradually reduced from 380 r / min to 180 r / min. During the reaction, the pH value is controlled at 7.1-7.5 and the ammonium concentration is controlled at 20-35 g / L until the particle size D50 grows to 19.0 μm, thereby obtaining a cobalt carbonate core layer.

[0178] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.6% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.5 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in according to the coating layer order. The thickness of each coating layer was about 0.35 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 6.9-7.3, and the ammonium concentration was controlled at 12-27 g / L until the aluminum-doped cobalt carbonate of Example 3 was prepared.

[0179] The surface scanning electron microscope morphology results of the cobalt carbonate secondary particles of Example 3 are shown in FIG18 .

[0180] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 830° C., a sintering time of 3.0 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 3.0 cm to prepare the multinary doped cobalt tetroxide of Example 3.

[0181] The surface scanning electron microscopy morphology of the cobalt oxide secondary particles of Example 3 is shown in FIG19 , and the cross-sectional scanning electron microscopy morphology thereof is shown in FIG20 .

[0182] 5. The cobalt trioxide obtained in Example 3 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 3.

[0183] Example 4

[0184] Example 4 provides a cobalt oxide precursor having a core layer doped with 0.95 wt% Al and two coating layers, wherein the molar ratio of the doping elements in each coating layer is close to the molar ratio of the doping elements in the cobalt solution of the coating layer during preparation, namely, n1: Co:Al:Ti = 0.87:0.03:0.10, and n2: Co:Al:Mg = 0.67:0.03:0.30. The preparation process is as follows:

[0185] 1. Aluminum sulfate and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with aluminum element, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt and aluminum elements in the solution is: Co:Al = 1:0.029; the concentration of the coating layer cobalt salt solution is mixed and configured according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 200 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 is prepared as a base solution.

[0186] 2. The prepared core layer cobalt salt solution and precipitant solution are simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the core layer cobalt salt solution is gradually increased from 2.5% / h to 6% / h of the available volume of the reactor, the flow rate of the precipitant solution is twice the flow rate of the cobalt salt solution, and the stirring speed is reduced from 380 r / min to 150 r / min. During the reaction, the pH value is controlled at 7.2-7.6 and the ammonium concentration is controlled at 24-39 g / L until the particle size D50 grows to 19.0 μm, thereby obtaining a cobalt carbonate core layer.

[0187] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.4% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.5 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in the order of the coating layers. The thickness of each coating layer was about 0.45 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 6.8-7.2, and the ammonium concentration was controlled at 10-25 g / L until the doped cobalt carbonate of Example 4 was prepared.

[0188] The surface scanning electron microscope morphology results of the cobalt carbonate secondary particles of Example 4 are shown in Figure 21.

[0189] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 780° C., a sintering time of 2.0 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 2.5 cm to prepare the multinary doped cobalt tetroxide of Example 4.

[0190] The surface scanning electron microscopy morphology of the cobalt oxide secondary particles of Example 4 is shown in FIG22 , and the cross-sectional scanning electron microscopy morphology thereof is shown in FIG23 .

[0191] 5. The cobalt trioxide obtained in Example 4 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 4.

[0192] Example 5

[0193] Example 5 provides a cobalt oxide precursor having a core layer doped with Al: 0.85wt% and Ni: 1.2wt% and three coating layers, wherein the molar ratio of the doping elements in each coating layer is close to the molar ratio of the doping elements in the cobalt solution of the coating layer during preparation, and is approximately n1: Co:Al:Zr = 0.95:0.03:0.02, n2: Co:Al:Y = 0.91:0.03:0.06, and n3: Co:Al:Mg = 0.67:0.03:0.30. The preparation process is as follows:

[0194] 1. Nickel sulfate, aluminum sulfate, and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with nickel and aluminum elements, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt, nickel, and aluminum elements in the solution is Co:Ni:Al=1:0.017:0.026; the concentration of the coating layer cobalt salt solution is mixed according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 190 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 is prepared as a base solution.

[0195] 2. The prepared core layer cobalt salt solution and precipitant solution are simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the cobalt salt solution is gradually increased from 2.5% / h to 6.0% / h of the available volume of the reactor, the flow rate of the precipitant solution is twice the flow rate of the cobalt salt solution, and the stirring speed is gradually reduced from 450 r / min to 250 r / min. During the reaction, the pH value is controlled at 7.0-7.4 and the ammonium concentration is controlled at 15-30 g / L until the particle size D50 grows to 11.5 μm, thereby obtaining a cobalt carbonate core layer.

[0196] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.5% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.5 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in the order of the coating layers. The thickness of each coating layer was about 0.35 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 6.8-7.2, and the ammonium concentration was controlled at 10-25 g / L until the aluminum-doped cobalt carbonate of Example 5 was prepared.

[0197] The surface scanning electron microscope morphology results of the cobalt carbonate secondary particles of Example 5 are shown in Figure 24.

[0198] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 750° C., a sintering time of 2.0 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 2.5 cm to prepare the multinary doped cobalt tetroxide of Example 5.

[0199] The surface scanning electron microscope morphology results of the cobalt trioxide secondary particles of Example 5 are shown in FIG25 .

[0200] 5. The cobalt trioxide obtained in Example 5 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 5.

[0201] Example 6

[0202] Example 6 provides a cobalt oxide precursor having a core layer doped with Al: 0.85wt% and Ni: 1.2wt% and three coating layers, wherein the molar ratio of the elements in each coating layer is close to the molar ratio of the metal elements in the cobalt solution of the coating layer during preparation, and is approximately n1: Co:Al:La = 0.94:0.03:0.03, n2: Co:Al:Ti = 0.88:0.03:0.09, and n3: Co:Al:Mg = 0.67:0.03:0.30. The preparation process is as follows:

[0203] 1. Nickel sulfate, aluminum sulfate, and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with nickel and aluminum elements, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt, nickel, and aluminum elements in the solution is Co:Ni:Al=1:0.017:0.026; the concentration of the coating layer cobalt salt solution is mixed according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 200 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 is prepared as a base solution.

[0204] 2. The prepared core layer cobalt salt solution and precipitant solution are simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the cobalt salt solution is gradually increased from 2.5% / h to 6.0% / h of the available volume of the reactor, the flow rate of the precipitant solution is twice the flow rate of the cobalt salt solution, and the stirring speed is gradually reduced from 400 r / min to 200 r / min. During the reaction, the pH value is controlled at 7.0-7.4 and the ammonium concentration is controlled at 15-30 g / L until the particle size D50 grows to 16.5 μm, thereby obtaining a cobalt carbonate core layer.

[0205] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.5% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.5 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in according to the coating layer sequence. The thickness of each coating layer was about 0.35 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 6.8-7.2, and the ammonium concentration was controlled at 10-25 g / L until the aluminum-doped cobalt carbonate of Example 6 was prepared.

[0206] The surface scanning electron microscope morphology results of the cobalt carbonate secondary particles of Example 6 are shown in Figure 26.

[0207] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 770° C., a sintering time of 2.0 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 2.5 cm to prepare the multinary doped cobalt tetroxide of Example 6.

[0208] The surface scanning electron microscope morphology results of the cobalt trioxide secondary particles of Example 6 are shown in FIG27 .

[0209] 5. The cobalt trioxide obtained in Example 6 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 6.

[0210] Example 7

[0211] Example 7 provides a cobalt oxide precursor having a core layer doped with 1.0 wt% Al and 1.0 wt% Ni and a single coating layer, wherein the molar ratio of the elements in the coating layer is close to the molar ratio of the metal elements in the cobalt solution of the coating layer during preparation, and n1 is approximately: Co:Al:La:Y:Ti:Mg=0.62:0.05:0.05:0.03:0.05:0.20. The preparation process is as follows:

[0212] 1. Nickel sulfate, aluminum sulfate, and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with nickel and aluminum elements, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 110 g / L, and the molar ratio of cobalt, nickel, and aluminum elements in the solution is Co:Ni:Al=1:0.010:0.022; the concentration of the coating layer cobalt salt solution is mixed according to the molar ratio of the coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 110 g / L; and an ammonium bicarbonate solution with a mass concentration of 200 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 is prepared as a base solution.

[0213] 2. The prepared core layer cobalt salt solution and precipitant solution are simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the cobalt salt solution is gradually increased from 2.5% / h to 6.0% / h of the available volume of the reactor, the flow rate of the precipitant solution is twice the flow rate of the cobalt salt solution, and the stirring speed is gradually reduced from 350 r / min to 150 r / min. During the reaction, the pH value is controlled at 7.0-7.4 and the ammonium concentration is controlled at 15-30 g / L until the particle size D50 grows to 20.0 μm, thereby obtaining a cobalt carbonate core layer.

[0214] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.5% / h of the available volume of the reactor, the flow rate of the precipitant solution was 1.5 times the flow rate of the cobalt salt solution, and the prepared coating layer cobalt salt solution was pumped in according to the coating layer sequence. The coating layer thickness was about 0.7 μm. During the reaction, the pH value was controlled at 6.8-7.2, and the ammonium concentration was controlled at 10-25 g / L until the aluminum-doped cobalt carbonate of Example 7 was prepared.

[0215] The surface scanning electron microscope morphology results of the cobalt carbonate secondary particles of Example 7 are shown in Figure 28.

[0216] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 820° C., a sintering time of 2.5 h, a rotary kiln tube rotation frequency of 1.0 r / min, and a material layer thickness of 3.0 cm to prepare the multinary doped cobalt tetroxide of Example 7.

[0217] The surface scanning electron microscope morphology results of the cobalt trioxide secondary particles of Example 7 are shown in Figure 29.

[0218] 6. The cobalt trioxide obtained in Example 7 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 7.

[0219] Example 8

[0220] Example 8 provides a cobalt oxide precursor having a core layer doped with 1.2 wt% Ni and 0.95 wt% Al and five coating layers, wherein the molar ratio of the doping elements in each coating layer is close to the molar ratio of the doping elements in the cobalt solution of the coating layer during preparation, namely, n1: Co:Al:Zr = 0.95:0.03:0.02, n2: Co:Al:La = 0.94:0.03:0.03, n3: Co:Al:Y = 0.91:0.03:0.06, n4: Co:Al:Ti = 0.88:0.03:0.09, and n5: Co:Al:Mg = 0.67:0.03:0.30. The preparation process is as follows:

[0221] 1. Nickel sulfate, aluminum sulfate, and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with nickel and aluminum elements, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt, nickel, and aluminum elements in the solution is: Co:Ni:Al=1:0.017:0.029; the concentration of the coating layer cobalt salt solution is mixed according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 190 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 is prepared as a base solution.

[0222] 2. The prepared cobalt salt solution and precipitant solution are simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the cobalt salt solution is gradually increased from 2.5% / h to 6.2% / h of the available volume of the reactor, the flow rate of the precipitant solution is twice the flow rate of the cobalt salt solution, and the stirring speed is gradually reduced from 350 r / min to 150 r / min. During the reaction, the pH value is controlled at 7.0-7.4, the ammonium concentration is controlled at 15-30 g / L, and the particle size D50 grows to 20.5 μm to obtain a cobalt carbonate core layer.

[0223] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.7% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.6 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in according to the coating layer order. The thickness of each coating layer was about 0.25 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 7.3-7.5, and the ammonium concentration was controlled at 20-35 g / L until the aluminum-doped cobalt carbonate of Example 5 was prepared.

[0224] The surface scanning electron microscope morphology results of the cobalt carbonate secondary particles of Example 8 are shown in Figure 30.

[0225] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 800° C., a sintering time of 2.5 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 3.0 cm to prepare the multinary doped cobalt tetroxide of Example 5.

[0226] The surface scanning electron microscope morphology results of the cobalt trioxide secondary particles of Example 8 are shown in Figure 31.

[0227] 5. The cobalt trioxide obtained in Example 8 and lithium carbonate were uniformly mixed at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 8.

[0228] Comparative Example 1

[0229] Comparative Example 1 provides a cobalt oxide precursor having a core layer doped with 1.0 wt% Al and two coating layers, wherein the molar ratio of the doping elements in each coating layer is close to the molar ratio of the doping elements in the cobalt solution of the coating layer during preparation, namely, n1: Co: Al = 0.95:0.05, and n2: Co: Al = 0.97:0.03, respectively. The preparation process is as follows:

[0230] 1. Aluminum sulfate and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with aluminum element, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt and aluminum elements in the solution is: Co:Al = 1:0.03; the concentration of the coating layer cobalt salt solution is mixed and configured according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 200 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 is prepared as a base solution.

[0231] 2. The prepared core layer cobalt salt solution and precipitant solution were simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the cobalt salt solution was gradually increased from 2.3% / h to 5.5% / h of the available volume of the reactor, the flow rate of the precipitant solution was twice the flow rate of the cobalt salt solution, and the stirring speed was gradually reduced from 380 r / min to 250 r / min. The particle size D50 grew to 19.0 μm to obtain a cobalt carbonate core layer.

[0232] 3. Change the process, reduce the flow rate of the cobalt salt solution to 2.4% / h of the available volume of the reactor, the flow rate of the precipitant solution is 1.5 times the flow rate of the cobalt salt solution, and pump the configured coating layer cobalt salt solution in the order of the coating layer. The thickness of each coating layer is about 0.45 μm. After the particle size is reached, replace the next coating layer solution. During the reaction, the pH value is controlled at 6.8-7.2 and the ammonium concentration is controlled at 10-25 g / L until the doped cobalt carbonate of Comparative Example 1 is prepared.

[0233] The surface scanning electron microscope morphology results of the cobalt carbonate secondary particles of Comparative Example 1 are shown in Figure 32.

[0234] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 740° C., a sintering time of 2.0 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 2.5 cm to prepare the multinary doped cobalt tetroxide of Comparative Example 1.

[0235] The surface scanning electron microscopy morphology of the cobalt oxide secondary particles of Comparative Example 1 is shown in FIG33 , and the cross-sectional scanning electron microscopy morphology thereof is shown in FIG34 ;

[0236] 5. The cobalt trioxide obtained in Comparative Example 1 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Comparative Example 1.

[0237] Comparative Example 2

[0238] Comparative Example 2 provides a cobalt tetroxide precursor doped with 1.2 wt% Ni and 0.85 wt% Al, which is not coated. The preparation process is as follows:

[0239] 1. Nickel sulfate, aluminum sulfate, and cobalt sulfate solutions were mixed to prepare a cobalt salt solution doped with nickel and aluminum elements, wherein the mass concentration of cobalt ions was 100 g / L and the molar ratio of cobalt, nickel, and aluminum elements in the solution was: Co:Ni:Al=1:0.017:0.026; and an ammonium bicarbonate solution with a mass concentration of 190 g / L was prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 was prepared as a base solution.

[0240] 2. The prepared cobalt salt solution and precipitant solution were simultaneously added to the reactor containing the base liquid to carry out the reaction. The flow rate of the cobalt salt solution was 2.5% / h of the available volume of the reactor, the flow rate of the precipitant solution was twice the flow rate of the cobalt salt solution, the stirring speed was reduced from 350 r / min to 150 r / min, and the particle size D50 grew to 20.5 μm to obtain a cobalt carbonate core layer.

[0241] The surface scanning electron microscope morphology results of the cobalt carbonate secondary particles of Comparative Example 2 are shown in FIG35 , and the cross-sectional scanning electron microscope morphology thereof is shown in FIG36 .

[0242] 3. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 750° C., a sintering time of 2.5 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 3.5 cm to prepare the multinary doped cobalt tetroxide of Comparative Example 2.

[0243] The surface scanning electron microscopy morphology of the cobalt oxide secondary particles of Comparative Example 2 is shown in Figure 37 (full view on the left, partial magnification on the right), and the cross-sectional scanning electron microscopy morphology is shown in Figure 38. As can be seen in the right figure of Figure 39, the cross-sectional surface shows a honeycomb structure composed of several small primary particles, which is caused by uneven aluminum doping. The Al composition of the cross-sectional coating micro-region of the cobalt oxide secondary particles was analyzed using an electron microprobe, and the results are shown in Figure 35. The Al distribution is uneven, with significant enrichment.

[0244] 4. The cobalt trioxide obtained in Comparative Example 2 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Comparative Example 2.

[0245] The indicators of the cobalt carbonate of each embodiment and comparative example are shown in Table 1.

[0246] Table 1 Indexes of cobalt carbonate in various embodiments and comparative examples

[0247] The indicators of the cobalt tetroxide of each embodiment and comparative example are shown in Table 2, wherein Examples 1 to 8 and Comparative Example 1 are cobalt tetroxide with different types of doping elements and doping contents, respectively, and the sintering process of Example 8 is different from that of Example 1, and its pore volume is larger; Comparative Example 2 is not coated with a coating layer, and its overall porosity and overall pore volume are lower, and the particle size is smaller.

[0248] Table 2 Indices of cobalt trioxide in various embodiments and comparative examples

[0249] Test example

[0250] The positive electrode materials of the above-mentioned embodiments and comparative examples were respectively dissolved in NMP solvent with conductive carbon black and polyvinylidene fluoride in a mass ratio of 85:10:5 under vacuum conditions to prepare a positive electrode slurry with a weight solid content of 80%. Positive electrode discs were then prepared by coating, drying, and punching. A lithium battery was then prepared in the order of positive electrode shell-positive electrode sheet-diaphragm-negative electrode sheet-stainless steel sheet-spring sheet-negative electrode shell. The electrolyte was 1 mol / L LiPF6 / EC:DMC (volume ratio of 1:1) with 10% (volume fraction) fluoroethylene carbonate (FEC). The diaphragm was a polypropylene microporous membrane. CR2032 button batteries of Examples 1 to 8 and Comparative Examples 1 to 2 were prepared, and electrochemical tests were performed at different rates using a Neware battery test system at room temperature. The battery performance of each embodiment and comparative example is shown in Table 3, 1C = 200mAh / g.

[0251] Table 3 Battery performance indicators of various embodiments and comparative examples

[0252] According to Table 1-3, compared with Comparative Examples 1-2, the battery prepared in Example 1-8 has both good discharge capacity and cycle performance, and has better 2C / 0.2C rate performance. Specifically:

[0253] 1. Compared with Example 1, the core layer of the cobalt tetroxide prepared in Example 2 is doped with manganese instead of nickel, and the capacity of the lithium ion battery prepared therefrom is slightly lower, but the cycle life is higher;

[0254] 2. Compared with Example 1, the coating layers of the cobalt tetroxide prepared in Examples 3, 4, 5, and 6 have fewer doping elements, forming a specific modified layer. The core layers of the cobalt tetroxide prepared in Examples 3 and 4 are not doped with Ni. The capacity and cycle retention rate of the lithium ion batteries prepared therefrom are slightly lower than those in Example 1, but are improved over Comparative Example 2. The particle size of the cobalt tetroxide prepared in Examples 5 and 6 is relatively small, and the combination of coating doping elements is adjusted, and the outermost layer contains Mg. Therefore, the capacity and cycle retention rate of the lithium ion batteries prepared therefrom are slightly lower than those in Example 1, but are slightly higher than those in Examples 3 and 4.

[0255] 3. Compared with Examples 3 and 4, the core layers of Examples 5 and 6 are doped with Ni, and their capacity is higher. At the same time, the number of doped layers is increased by one, and the outermost layers are doped with Mg, and their rate performance is better.

[0256] 4. Compared with Example 1, the cobalt tetroxide coating layer prepared in Example 7 is one layer, and multiple elements are doped at the same time and the doping amount is fine-tuned. Such adjustment results in an excessively high content of doping elements in the shell layer, a decrease in doping uniformity, and thus a decrease in the overall electrical performance; the cobalt tetroxide prepared in Example 8 has an increased Al doping amount. The addition of Al element can stabilize the crystal structure, and the lithium ion battery prepared therefrom has an improved cycle retention rate, but the excessive Al element doping has a certain effect on the capacity, so the discharge capacity is slightly lower.

[0257] 5. Compared with Examples 1-8, the cobalt trioxide prepared in Comparative Example 1 is provided with a coating layer, but the cobalt content of the coating layer increases layer by layer and no other doping elements except Al are added for modification. 4+ Dissolution increased, and the stirring speed did not decrease with the growth of particle size, and a certain speed was continuously maintained. The overall porosity of the obtained cobalt carbonate particles was low, the specific surface area was low, and the overall pore volume was low. The corresponding cycle retention rate of the lithium-ion battery was deteriorated. The capacity and cycle retention rate of the battery were poor compared with those of Examples 1-8. However, the setting of the coating layer improved the surface structure stability of the material. Therefore, the capacity and cycle retention rate of Comparative Example 1 were higher than those of Comparative Example 2, but lower than those of each embodiment.

[0258] 6. Compared with Examples 1-8, the cobalt tetroxide prepared in Comparative Example 2 has no coating layer, and the doping elements in the core layer are unevenly distributed, resulting in a decrease in the capacity and cycle retention rate of the corresponding lithium-ion battery.

[0259] 7. Compared with Comparative Examples 1 and 2, the cobalt oxide-derived cathode materials prepared in Examples 1 to 8 all exhibited 2C / 0.2C rate performance exceeding 97.9% at 3.6-4.55V, significantly improving rate performance. The rate performance of Examples 1, 2, and 3 all exceeded 98%, demonstrating that the doping of the coating layer achieved the desired effect. Example 3 employed La and Zr doping, which significantly improved ion mobility and rate performance. Example 4 employed Ti and Mg doping, which formed continuous channels, enhancing ion transport efficiency and rate performance.

[0260] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present disclosure.

[0261] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not other features, the combination of features from different embodiments is intended to be within the scope of this disclosure and to form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of this disclosure and should not be construed as an admission or any form of implication that such information constitutes prior art already known to those skilled in the art. Industrial Applicability

[0262] In summary, the cobalt carbonate and cobalt oxide provided by the present disclosure include a core layer and a coating layer coated outside the core layer. By gradient doping the cobalt oxide particles with Al as a whole, and the Al doping amount of the core layer is higher than that of the coating layer, the crystal structure stability of the LCO material can be improved and the cycle performance can be improved. For cobalt carbonate, the Al element exists in the form of amorphous aluminum hydroxide during the crystallization process. The lower aluminum content in the coating layer is conducive to controlling the hydrolysis of amorphous aluminum hydroxide during centrifugal washing; and the porosity and pore volume of the coating layer are lower than those of the core layer, which is conducive to inhibiting the hydrolysis of amorphous aluminum hydroxide in the core layer, thereby improving the uniformity of aluminum element distribution.

[0263] Furthermore, it is understood that the cobalt oxide, cobalt carbonate, and preparation methods, cathode materials, and lithium-ion batteries of the present application are reproducible and can be used in a variety of industrial applications. For example, the cobalt oxide, cobalt carbonate, and preparation methods, cathode materials, and lithium-ion batteries of the present application can be used in the field of lithium-ion batteries.

[0264] The method for obtaining the cross section of the secondary particles of the precursor of the present invention is: cutting the powder granular sample of the present invention by ion beam to obtain the cross section, and then taking a picture with an electron microscope to obtain a cross section SEM picture.

[0265] As shown in the cross-sectional SEM photograph of FIG1 , the secondary particles are divided into a plurality of radially arranged annular regions on the periphery as the outer shell, and the porous region within the annular region as the inner core.

Claims

1. A cobalt trioxide, characterized in that: The cobalt oxide comprises a core layer and a coating layer coated outside the core layer; the core layer and the coating layer are both doped with Al, and the Al doping content of the core layer is higher than the Al doping content of the coating layer.

2. The cobalt tetraoxide according to claim 1, characterized in that The cobalt content of the cobalt tetroxide decreases layer by layer from the core layer to the coating layer.

3. The cobalt trioxide according to claim 1 or 2, characterized in that The cobalt oxide satisfies at least one of the following conditions A to H: A. The coating layer of the cobalt trioxide is 1 to 5 layers; B. The ratio of the mass of Al doped in the core layer of the cobalt oxide to the total mass of metal in the core layer of the cobalt oxide is 0.40 to 1.20 wt %; C. The ratio of the mass of Al doped in the coating layer of the cobalt oxide to the total mass of metal in the cobalt oxide is: 0.02-0.40wt%; D. When the coating layer of the cobalt oxide is one layer, the ratio of the molar amount of cobalt in the coating layer of the cobalt oxide to the molar amount of the total metal in the coating layer of the cobalt oxide is ≤70 mol%; E. When the number of the coating layers of the cobalt oxide is 2 to 5, the ratio of the molar amount of cobalt in the outermost layer of the cobalt oxide coating layer to the molar amount of the total metal in the outermost layer of the cobalt oxide coating layer is ≤70 mol%; F. The diameter of the core layer of the cobalt oxide is 5.0 to 18.0 μm; G. When the coating layer of the cobalt oxide is one layer, the thickness of the coating layer of the cobalt oxide is 0.10 to 1.0 μm; H. When the number of the coating layers of the tricobalt tetroxide is 2 to 5, the thickness of a single layer in the coating layers of the tricobalt tetroxide is 0.10 to 1.0 μm.

4. The cobalt tetraoxide according to any one of claims 1 to 3, characterized in that The cobalt oxide satisfies at least one of the following conditions I to L: I. The core layer of the cobalt oxide further includes Ni and / or Mn; J. When condition I is met, the ratio of the mass of Ni and Mn doped in the core layer of the cobalt oxide to the total metal mass in the core layer of the cobalt oxide is independently 0.10 to 3.00 wt %; K. The cobalt oxide coating layer further includes one or more doping elements selected from the group consisting of Mg, Ti, La, Zr, Y, Ca, Sr, and Ba; L. When condition K is met, the ratio of the mass of other doping elements except Al in the coating layer of the cobalt oxide to the total metal mass in the cobalt oxide is independently 0.01 to 0.40 wt%.

5. The cobalt trioxide according to claim 4, characterized in that When the cobalt tetraoxide satisfies condition K, When the coating layer is two layers, the coating layer is divided into an inner layer and an outer layer, the inner layer of the coating layer further includes one or more of Zr, La, Ca, Ba, Y, Ti, and Sr; the outer layer of the coating layer further includes one or more of Mg, Zr, Ti, and Sr; When the coating layer has 3-5 layers, the coating layer is divided into an inner layer, an intermediate layer and an outer layer, the inner layer and the outer layer are respectively 1 layer, the inner layer of the coating layer also includes one or more of Zr, La, Ca, and Ba; the intermediate layer of the coating layer also includes one or more of La, Zr, Y, Ti, and Sr; the outer layer of the coating layer also includes one or more of Mg, Zr, Ti, and Sr.

6. The cobalt trioxide according to claim 5, characterized in that The cobalt oxide satisfies at least one of the following conditions M to Q: M. The porosity of the core layer of the cobalt oxide is 5.5-9.5%, and the overall porosity of the cobalt oxide is 4.5-7.5%; N. The pore volume of the core layer of the cobalt tetraoxide is 0.004 to 0.015 cm 3 / g, the overall pore volume of the cobalt tetraoxide is 0.002-0.080cm 3 / g; O. The D50 of the cobalt oxide is 5.5 to 23.0 μm; P. The tap density of the cobalt tetraoxide is 2.0 to 3.0 g / cm 3 ; Q. The specific surface area of ​​the cobalt tetraoxide is 2.0 to 15 m 2 / g.

7. A cobalt carbonate, characterized in that The cobalt carbonate comprises a core layer and a coating layer coated outside the core layer; the core layer of the cobalt carbonate and the coating layer of the cobalt carbonate are both doped with Al, and the Al doping content of the core layer of the cobalt carbonate is higher than the Al doping content of the coating layer of the cobalt carbonate.

8. Cobalt carbonate according to claim 7, characterized in that The cobalt content of the cobalt carbonate decreases layer by layer from the core layer of the cobalt carbonate to the coating layer of the cobalt carbonate.

9. Cobalt carbonate according to claim 8, characterized in that The cobalt carbonate satisfies at least one of the following conditions a to l: a. The coating layer of cobalt carbonate is 1 to 5 layers; b. The ratio of the mass of doped Al in the core layer of the cobalt carbonate to the total mass of metal in the core layer of the cobalt carbonate is: 0.26 to 0.80 wt %; c. The ratio of the mass of doped Al in the coating layer of the cobalt carbonate to the total mass of metal in the cobalt carbonate is: 0.01 to 0.27 wt %; d. When the coating layer of cobalt carbonate is one layer, the ratio of the molar amount of cobalt in the coating layer of cobalt carbonate to the molar amount of the total metal in the coating layer of cobalt carbonate is ≤70 mol%; e. When the number of the cobalt carbonate coating layers is 2 to 5, the ratio of the molar amount of cobalt in the outermost layer of the cobalt carbonate coating layer to the molar amount of the total metal in the outermost layer of the cobalt carbonate coating layer is ≤70 mol%; f. The diameter of the core layer of the cobalt carbonate is 8.0 to 23.0 μm; g. When the coating layer of cobalt carbonate is 1 layer, the thickness of the coating layer of cobalt carbonate is 0.15 to 1.5 μm; h. When the coating layer of cobalt carbonate is 2 to 5 layers, the thickness of a single layer in the coating layer of cobalt carbonate is 0.15 to 1.5 μm; i. The core layer of the cobalt carbonate further includes Ni and / or Mn; j. When condition i is met, the ratio of the mass of Ni and Mn doped in the core layer of the cobalt carbonate to the total metal mass in the core layer of the cobalt carbonate is independently 0.07 to 2.00 wt %; k. The cobalt carbonate coating layer further includes one or more doping elements selected from Mg, Ti, La, Zr, Y, Ca, Sr, and Ba; 1. When condition k is met, the ratio of the mass of other doping elements in the coating layer of the cobalt carbonate except Al to the total mass of metal in the cobalt carbonate is independently 0.01 to 0.30 wt%.

10. The cobalt carbonate according to claim 9, characterized in that When the cobalt carbonate satisfies condition k, When the coating layer is two layers, the coating layer is divided into an inner layer and an outer layer, the inner layer of the coating layer further includes one or more of Zr, La, Ca, Ba, Y, Ti, and Sr; the outer layer of the coating layer further includes one or more of Mg, Zr, Ti, and Sr; When the coating layer has 3-5 layers, the coating layer is divided into an inner layer, an intermediate layer and an outer layer, the inner layer and the outer layer are respectively 1 layer, the inner layer of the coating layer also includes one or more of Zr, La, Ca, and Ba; the intermediate layer of the coating layer also includes one or more of La, Zr, Y, Ti, and Sr; the outer layer of the coating layer also includes one or more of Mg, Zr, Ti, and Sr.

11. The cobalt carbonate according to claim 10, characterized in that The cobalt carbonate satisfies at least one of the following conditions m to q: m. The porosity of the core layer of the cobalt carbonate is 15 to 25%, and the overall porosity of the cobalt carbonate is 14 to 25%; n. The pore volume of the core layer of the cobalt carbonate is 0.08 to 0.30 cm 3 / g, the overall pore volume of the cobalt carbonate is 0.05-0.25cm 3 / g; o. The D50 of the cobalt carbonate is 8.7 to 30.0 μm; p. The specific surface area of ​​the cobalt carbonate is 50 to 150 m 2 / g; q. The tap density of the cobalt carbonate is 1.5 to 2.0 g / cm 3 .

12. A method for preparing cobalt carbonate, characterized in that: include: The core layer cobalt salt solution and the precipitant solution are added to a reactor containing a bottom liquid for reaction, wherein the flow rate of the core layer cobalt salt solution increases with the increase of the particle size of the material, the flow rate of the precipitant solution increases with the increase of the flow rate of the core layer cobalt salt solution, and the stirring speed of the reactor decreases with the increase of the particle size of the material, and the reaction is continued until the particle size D50 is 8.0 to 23.0 μm, to obtain a cobalt carbonate core layer; The coating layer cobalt salt solution and the precipitant solution are sequentially added into the reaction kettle containing the cobalt carbonate core layer to react until the growth of each coating layer is completed to obtain cobalt carbonate.

13. A method for preparing cobalt trioxide, characterized in that: The method is obtained by sintering the cobalt carbonate prepared by the cobalt carbonate according to any one of claims 7 to 11 or the method for preparing cobalt carbonate according to claim 12.

14. A positive electrode material, characterized in that: Lithium cobalt oxide obtained by calcining the cobalt trioxide according to any one of claims 1 to 6 and a lithium source.

15. The positive electrode material according to claim 14, characterized in that The molar ratio of the lithium source to the cobalt tetroxide is (1-1.05):

1.

16. The positive electrode material according to claim 14, characterized in that The calcination temperature is 900° C. to 1200° C., and the calcination time is 20 to 30 hours.

17. A lithium ion battery, characterized in that: The raw materials include the positive electrode material described in any one of claims 14 to 16.

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